Variations in maternal behavior regulate the development of neural systems that mediate the expression of behavioral and endocrine responses to stress in the rat (see Liu et al., Science, 1997; Caldji et al., 1998 PNAS), as well as maternal behavior (Francis et al, 1999). Recent findings (Francis et al, 1999) suggest that these effects provide an example of the behavioral transmission of traits from one generation to the next. The next question concerns the origins of these individual differences in maternal behavior. Our primary goal in these studies is to understand the neurobiological basis for the relationships that exist between environmental stimuli, individual differences in parental behavior and the development of behavioral and endocrine responses to stress. The hypothesis which drives this grant attempts to explain these environmental effects in terms of the development of neural systems underlying fearfulness as well as those which mediate parental care. The experiments proposed here are designed to address the three principle tenets of this hypothesis: 1) that individual differences in maternal behavior are inherited via a behavioral mode of transmission, 2) that variations in maternal care are associated with individual differences in neural systems that mediate the expression of maternal behavior, and 3) that the critical features of these systems involve estrogen-oxytocin interactions which, in turn, regulate dopamine activity. Specifically we propose that maternal care influences the development of estrogen receptor gene expression in the medial preoptic area, increasing the sensitivity of this structure to oxytocin and providing a basis for subsequent oxytocin-induced increases in dopamine release in the nucleus accumbens.